In prior proposed systems for the magnetic testing of parts for defects therein, difficulties have been experienced in testing of surface portions of a part which are irregular in contour or which are inside of a part to present difficulties with respect to access thereto. An example is drill pipe in which transverse fatigue cracks and corrosion pitting are oftentimes developed on the internal surface of the type especially in the end regions in which the pipe is formed with coupling portions to permit the end of one pipe section to be joined to the end of another. Prior art systems for testing of drill pipe and the like have been quite complicated, expensive, difficult to operate and not always reliable. Systems have been proposed for optical scanning which is not capable of detecting some types of serious defects, especially when the surface of the pipe is rusted or corroded. Systems have also been proposed using probes moved around on the inside of the pipe to scan the internal surface for defects, presenting problems especially with respect to obtaining the required scanning movement of the probe while maintaining the proper spacing relationship between the probe and the internal surface of the part.
There also have been prior art systems using a magnetic tape or other magnetizable material placed in contact with the surface of a part. Generally such systems have been designed for the testing of external or otherwise readily accessible surfaces. However, in the De Forest U.S. Pat. No. 2,764,733 issued Sept. 25, 1956, there is a suggestion in FIG. 6 of placing a tube inside a pipe, the tube being of an elastomeric material such as rubber with magnetizable particles such as iron or iron oxide particles dispersed therein and being inflated by compressed air to contact the internal surface of the part. The manner of magnetizing the part is not specifically disclosed.